Underwater Meadows


Widgeon grass. Photos in this post courtesy of chesapeakebay.net

Below the waves of the Chesapeake Bay, trillions of tiny life forces are moving. They flash translucent fins, their claws snap at passing minnows. They creep from their white shells and unfold their feet, waving at passing morsels of plankton. They release a whoosh of water, and with it, a smoke ring of sediment.  Although each takes a different shape, these oyster, fish, crab, snail, mussel, and barnacle residents of the Bay proper all have something in common- they are breathing. Their hearts beat their blue or black foreign blood, and tiny lungs force oxygen out of their atmosphere of brackish water and swirling sand. The source of much of this essential element is all around, waving in rhythm with the ceaseless currents: grasses. Dense underwater meadows throughout the Bay are steadily taking in carbon dioxide, sunlight, and nutrients, and releasing oxygen’s breath of vitality into the surrounding waters.


Grasses in the shallows off of Poplar Island.

There is much talk about these grasses today, due to their integral role in the balance of the Bay’s equilibrium. This submerged aquatic vegetation (or SAV for short) supplies not only oxygen, but food, habitat, and tidal buffers for the myriad residents that populate their green, verdant kingdom. Like trees in a forest, SAV in the Chesapeake shape their environment and the animals that have adapted to dwell symbiotically under their protective canopy. Where the grass grows, the Chesapeake’s animal populations thrive and the water slows, dropping sediment and gaining clarity. But when those meadows shrink, the bottom of the Bay becomes a cloudy wasteland of unproductive mud. Without Bay grasses, crabs lose their spawning grounds, migratory waterfowl go hungry, perch gasp for air, and waders at the water’s edge lose sight of their toes once their knees get wet. SAV have a huge impact on the health of the Chesapeake- quite a feat for something that seems so easy to ignore.

A carp peeks from a carpet of bottom grasses.

Knowing this, it seems no surprise that as the Chesapeake Bay grasses decline for the third year, so too has the population of the Bay’s blue crabs. The Baltimore Sun reports:

“An aerial survey flown from late spring to early fall last year found 48,191 acres of submerged vegetation, down 21 percent from the extent of grasses seen in 2011, according to scientists from Maryland and Virginia.

It was the third straight year of reported declines, following a 21 percent drop in 2011 and a 7 percent dip in 2010. Since hitting a peak of sorts in 2009, the bay’s grasses have shrunk to a level last seen in 1986, shortly after scientists began conducting annual surveys of the bay’s grasses.

Scientists attributed the losses in large part to an extended run of unfavorable weather, with extreme summer heat in 2010 killing off lower bay grasses and heavy rains and tropical storms knocking back vegetation in the upper and middle bays.  Hurricane Irene and Tropical Storm Lee flushed millions of tons of sediment down the Susquehanna and other rivers, turning the bay murky brown for months afterward.”

A crab in the grass.

For blue crabs, the loss of Bay grasses has been a severe blow. Underwater meadows provide food and shelter for crab during the summer, when the courtship and reproductive season are well underway.  But summer is also a time when grasses are particularly susceptible to the warm-weather algal blooms, which block sunlight and stunt the growth of the grass beds. Nutrients from septic tanks, from farm fields and pastures, and from car exhaust that have collected in the Chesapeake’s tributaries throughout the spring encourage the growth of these malignant blooms, which expand with oily rapidity as temperatures rise. On the Bay’s bottom, shaded over, the oxygen-producing grasses wither, leaving blue crabs homeless and focused on survival rather than romance.

It’s a vicious cycle, but one that reminds us how deeply and irrevocably interconnected the Chesapeake’s life forms are. For a healthy Bay, one that is productive, clear, and vibrant, we must look to maintain the lawn. Not the clipped, manicured kind in our yards, stretching to the water’s edge, but the kind down below the waves, with roots in the Chesapeake’s sandy bottom where the crab couples hide to find some privacy.

Want to track the rise and fall of Chesapeake grasses over time? Check out this AMAZING time-lapse interactive map, over at the Chesapeake Bay Program: